package com.leetcode;

import java.lang.reflect.Array;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.Stream;

/**
 * @Author: chenyuan.wang
 * @Description: TODO 两数之和
 * @Date: 2019/3/22 16:41
 * @Version 1.0
 */
public class TwoSum {
    /**
     * 给定一个整数数组 nums 和一个目标值 target，请你在该数组中找出和为目标值的那 两个 整数，并返回他们的数组下标。
     * <p>
     * 你可以假设每种输入只会对应一个答案。但是，你不能重复利用这个数组中同样的元素。
     * <p>
     * 示例:
     * <p>
     * 给定 nums = [2, 7, 11, 15], target = 9
     * <p>
     * 因为 nums[0] + nums[1] = 2 + 7 = 9
     * 所以返回 [0, 1]
     */
    public static void main(String[] args) {
        int[] nums = {1, 3, 4, 6};
        int targer = 9;
        int[] ints = twoSum(nums, targer);
        System.out.println(Arrays.toString(ints));
    }

    public static int[] twoSum(int[] nums, int target) {
        for (int i = 0; i < nums.length; i++) {
            for (int j = i + 1; j < nums.length; j++) {
                if (nums[j] == target - nums[i]) {
                    return new int[]{i, j};
                }
            }
        }
        throw new IllegalArgumentException("No two sum solution");
    }

    public static int[] twoSum2(int[] nums, int target) {
        Map<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < nums.length; i++) {
            int complement = target - nums[i];
            if (map.containsKey(complement)) {
                return new int[]{map.get(complement), i};
            }
            map.put(nums[i], i);
        }
        return null;
    }
}

/**
 * leekcode最快
 */
class Solution {
    int size = 2048;
    int[] map = new int[size];
    int length = 2047;
    int index;

    public int[] twoSum(int[] nums, int target) {
        for (int i = 0; i < nums.length; i++) {
            index = nums[i] & length; //

            if (map[index] != 0) {
                return new int[]{map[index] - 1, i};
            } else {
                map[(target - index) & length] = i + 1;
            }
        }
        throw new IllegalArgumentException("No two sum solution");
    }
}
